Synthetic turf material and method of making same

ABSTRACT

TURF-LIKE SURFACING FORMED FROM SOFT ELASTOMERIC BASE LAYER ADHERED TO RIGID SUBSTRATE FORMED FROM 100% SOLIDS POLYURETHANE HAVING SHORE A2 HARDNESS OF BETWEEN 5 AND 404 AND CONTAINING 15 TO 75% BY VOLUME OF VOIDS, THE MAJOR PORTION OF WHICH ARE IN THE 1/16 TO 1/4 DIAMETER RANGE AND TOP SURFACE OF TOUGH PILE FABRIC ADHERED BY MEANS OF ADHESIVE WHICH PENETRATES THE BACK OF SAID FABRIC AND EMBEDS THE LOWER PORTION OF THE FIBERS THEREIN, THE BASE LAYER PROVIDING BOTH VISCOUS AND ELASTIC RESPONSE TO COMPRESSION AND BEING CAPABLE OF SLOW RECOVERY FROM INDENTATION OVER A 2- TO 20-SECOND PERIOD.

Aug. 3, 1971 T BUCHHOLTZ ETAL 3,597,297

.A SYNTHETIC TURF MATERIAL AND METHOD 0F MAKING SAME Filed Jim@ 25, 1968F/q. f

United States Patent O U.S. Cl. 161--21 10 Claims ABSTRACT F THEDISCLOSURE rTurf-like surfacing formed from soft elastomeric base layeradhered to rigid substrate formed from 100% solids polyurethane havingShore A2 hardness of between 5 and 404 and containing to 75% by volumeof voids, the major portion of which are in the 1/16 to 1A: diameterrange and top surface of tough pile fabric adhered by means of adhesivewhich penetrates the back of said fabric and embeds the lower portion ofthe fibers therein, the base layer providing both viscous and elasticresponse to compression and being capable of slow recovery fromindentation over a 2- to 20-second period.

This invention relates to novel very soft elastomeric materialscontaining large voids, to synthetic turf material utilizing the same asan integral component thereof, and to a method for preparing the same.More particularly the invention relates to synthetic turf materialswhich utilize very low durometer polyurethane elastomers containingvoids, which may be formed by crushing of relatively large frangiblefillers contained therein as a base layer.

Various attempts have been made to produce artificial turf having agrass-like surface for indoor or outdoor recreational and sportsactivities, or for use as a surfacing in other areas which receive hardwear. The currently most widely used form of such turfs is of thegeneral type shown in U.S. Pat. 3,332,828, issued July 25, 1967, toFaria et al. Turfs are described in this patent which are formed byapplying a conventional foam backing to the substrate by means of anadhesive such as a latex, and then applying a tufted fabric over thefoam backing by means of a latex. Such constructions, however, sufferfrom several shortcomings, one of which is difficulty of adhesion tomany substrates, particularly natural soils or gravel; the most seriousshortcoming is the stiffness or hardness of the surface, even thoughcovered by tufted fibers. The problem is particularly severe whereoutdoor surfacing is desired because, in order to minimize absorption ofwater, the base foam is disclosed as being of a closed cell structure.Chemically blown closed cell foams of this type, however, have astiffness which is unwanted in the base layer of a turf type surfacing.Because of the difficulty of applying the base layers to asphalt orother substrates by means of Water or solvent based adhesives, it hasbecome the actual practice to mechanically hold the surfacing in place.This is usually done by fastening the edges of the surfacing intotrenches along the edges of the field to hold the surfacing tightly overthe field.

It is an object of the present invention to provide resilient syntheticsurfaces which resemble natural turf in appearance and performance,which are weather resistant. Such surfaces can be formed in accordancewith the invention which are uniform and provide high traction. Surfacesof this invention are more durable than natural turf and previouslyproposed synthetic turfs, and thus can be maintained at low cost.

In accordance with the present invention, turf type surfacing isprovided with an extremely soft yet resilient 3,597,297 Patented ug. 3,1971 elastomeric base layer of a crosslinked polyurethane having ShoreA2 durometers in the range of 5 to 40. These base materials are capableof being pushed down to onethird or less of their original volume byfinger pressures, and exhibit a gradual but substantially full recoveryover a period of 2 to 20 seconds and preferably 5 to l5 seconds afterthe application of such pressure. The resilient base layer is formedfrom a castable liquid material `which can be poured and cured in placeon any suitable substrate such as concrete, asphalt, conventionalflooring materials, and the like. The reaction mixture contains afrangible preferably hollow filler which is crushed after cure of thereaction mixture.

The finished turf surfaced material is formed by coating the soft baselayer with additional liquid polyurethane material which functions as anadhesive to secure a top turf type surfacing to the base. The turfsurfacing is a stretchable open fabric which may be either a woven,non-woven, or preferably a knitted backing to which fibers are secured.Knitted fabrics which are stretchable by virtue of their constructionare prferred, but fabrics formed from elastic bers can be substituted.The open backed pile fabric is pressed into the reaction mixture whileit is still liquid so that the reaction mixture penetrates the fabricportion of the pile material. The porous fabric and the lower ends ofthe pile fibers thus become embedded in the curing polyurethane mixture.The finished synthetic turf has an improved softness such that it ispossible t0 jump with the full weight of ones body on the knees withoutshock or injury to the knees or legs. Thus, when used for athleticplaying fields such as football fields, the synthetic turf of thisinvention minimizes leg injuries, which have become an increasingproblem for athletes. Even though the finished surfacing is very soft,it is durable and can withstand the action of cleated or spiked shoesduring rough athletic play in addition to being weather resistant.Because of the dead soft or slow recovery characteristic of thesubstrate layer, a quality similar to natural, which yields and receivesa permanent impression, is provided. Synthetic turfs having a trulyelastic recovery tend to be too rubbery to the extent that they workback against the action of cleats or shoes, thus producing an unwantedspringiness. In contrast the substrate of this invention has the abilityto yield a great amount and remain deformed for a period of time, thusresembling natural soils, but also has the ability to gradually recoverits original shape over a period of seconds.

The invention will be further explained with reference to theaccompanying drawing, wherein:

FIG. 1 is a cross-sectional view illustrating the crushing step in thepreferred mode of forming the base layer 0f this invention, and

FIG. 2 is a cross-sectional view of the finished synthetic turfconstruction of this invention.

Referring more particularly to FIG. l, there is seen a base layer 10preferably formed by pouring a liquid polyurethane-forming reactionmixture onto a solid substrate 12, which is preferably asphalt orconcrete, and curing the same in situ to a solid state. Base layer 10contains a frangible filler 14 which is crushed by means of any suitabledevice 16 for applying high localized pressures to the base layer. Aftercrushing of the filler 14, voids 18 are provided in the base layer.

As seen in FIG. 2, the finished surface is provided by adhering a pilefabric 20 to the top of the base layer 10. Pile fabric 20 consists of anopen base fabric 22 and a pile fabric 24 which simulates natural turf.The pile fabric 20 is adhered to base layer 10 by means of an adhesive26 which uniformly coats the base layer 10 and penetrates the backingfabric 22 and preferably also surrounds the lower ends of the fibers 24.

ICC

The resilient base layer for the surfacing of the present invention isformed from pourable liquid reaction mixtures of organic polyisocyanatesand coreactive materials which contain active hydrogen atoms (asdetermined by the well-known Zerewitinoff method), said coreactantsbeing preferably organic polyols or blends of organic polyols andorganic polyamines which contain a catalyst, if necessary, so that thereaction mixture will harden from a liquid state to a solid elastomericstate under ambient temperatures and pressures. The reaction mixturescontain approximately equivalent quantities, i.e., 0.7:l to about 1.2:1of isocyanate groups to active hydrogens. The preferred reactionmixtures react rapidly at ambient temperatures so that within an hour orless the liquid mixture has cured to a slump resistant state. Thereaction mixture is mixed shortly before casting. Known proportioningand mixing equipment is preferably used for mixng the components anddispensing the reaction mixture.

The preferred polyisocyanates are aromatic diisocyanates such as toluenediisocyanate, diphenylmethane diisocyanate, or chlorophenylene2,4-diisocyanate. It will be apparent to those skilled in the art,however, that aliphatic, cycloaliphatic, or heterocyclic polyisocyanatesor mixtures thereof can be substituted.

The preferred coreactant for the polyisocyanate is a polyalkylene etherpolyol, preferably a polypropylene ether glycol either alone or mixedwith an aromatic polyamine such as 4,4methylene bis 2-chloroaniline(MOCA). Small amounts of other polyols such as polyester polyols orpolyether ester polyols can be substituted, but these are not preferredbecause of the greater hydrolyzin'g tendencies of the resultingpolymers.

It is desirable to introduce some components having three or morereactive groups or atoms in order to provide some crosslinking as wellas chain extension of the reaction mixture. This is readily accomplishedby including some triisocyanate, triol, tetrol, pentol, triamine, etc.in the reaction mixture. It is usually preferable to prereact thepolyisocyanate lwith a small amount of polyol to reduce the toxicity ofthe material and to improve the mixing ratio of the two-part system fromwhich the base layer is cast.

Any known catalyst for the polyurethane reaction can be used. Thepreferred catalysts are soluble metal compounds, for example, mercury,lead, or tin salts of carboxylic acids or organo tin compounds. Thepreferred catalysts are organo rnercuric compounds such as phenylmercurio acetate or phenyl mercuric hydroxide. The reaction mixturepreferably contains at least 0.05% by weight of such a catalyst, or moreas desired to produce the desired rapid ambient temperature cure rate.

The hardness of the rubber is controlled within the 5 to 40 Shore A-2durometer range by adding to the reaction mixture predetermined amountsof a chain terminating agent such as butyl Cellulose (mono-butyl etherof ethylene glycol), butyl carbitol (mono-butyl ether of diethyleneglycol), oleyl alcohol, ethylene glycol monoethyl ether, or similarmono-functional alcohols. Other compounds having a single activehydrogen can also be substituted.

The preferred frangible filler for forming the voidcontaining base layeris perlite. Other suitable materials are frangible hollow glass orplastic beads, expanded vermiculite, or even breakfast cereals. However,inorganic low density frangible llers are preferred in order to optimizethe weather stability and fungal resistance of the structure. 'Ihefrangible filler preferably is a diameter range between about 1&6 and1A, inch. The elastomer can also in addition contain some voids of asmaller size if desired. In practice such voids usually result from theentrainment of air with ya crushable filler, from CO2 generation due tomoisture in the reaction mixture, or both. The finished base layershould contain between about and 75 percent by volume of voids. Optimumresults have been obtained in the to 45 percent range.

The optimum void fraction will vary slightly among various systems ofthe invention depending on the size distribution of the voids, and thedeformation characteristics of the elastomer. It appears that voidswhich are partially or slightly interconnected so that a bellows-typeeffect is achieved during localized compression of the elastomer arepreferable because this bellows effect seems to contribute to the slowregain characteristic of the material by damping of the elastic recoveryspeed of the elastomer. While it is preferred to form the base layer bycrushing of a frangible filler, it will be understood that equivalentstructures can be formed by mechanical whipping in of the voids to thesame volume content, preferably to form sli-ghtly interconnected voidsof the type achieved by the addition and crushing of a frangible filler.

Where a frangible filler is used, a device which produces suicientlocalized pressure to cause thorough crushing of the filler can be used.For example, hammering or rolling devices can be employed so long as thepolymer is not torn or otherwise injured. One suitable device is aweighted machine resemblng an agricultural disc in which the discs areblunt edged rather than sharp.

When the voids are made in the material by means of a frangible filler,it is preferred that the polymer contain an anti-settling agent. Suchagents include finely divided materials, for example, finely dividedsilica or clays commercially available for this purpose, but we preferto use small diameter, short asbestos fibers. Such agents providethixotropy to the system and thus prevent floating of .the filler in theresin and assure a uniform distribution of voids in the base layer.

Because of the very soft and deformable nature of the base layer of thisinvention, it has been found that the tufted fabric `applied to form thetop surface should also be of a highly stretchable nature. In order toform a durable composite structure, the fabric backing to which thefibers are attached must be capable of fiexing with the substrate. Thepreferred backing fabric is a circular knit polyester (preferablypolyethylene terephthalate) fabric to which the grass simulating fibersare secured, preferably by looping. Other fibers or yarns can be usedfor forming the knitted fabric. |For example, nylon, polypropylene,rayon, or other fabrics can be substituted. The projecting fibers shouldbe formed from durable weather resistant fibers, such as nylon,polypropylene, polyesters, or similar tough fibers can be used.Preferably the fibers are crimped to provide resilience and mattingresistance to the tufted surface. The fibers can be dyed any desiredcolor, but green is usually preferred to simulate grass. It will Ibeapparent that any dyes used should be color fast under weather exposureconditions. Ultraviolet light absorbers may also be added to the fibersas needed.

It is important that the fabric backing for the pile material be capableof stretching at least 50% in any direction. Most of this stretchabilityis provided by the manner in which the fabric is knitted. The preferredfabrics are capable of elongation of at least in at least one direction.Fabrics which do not elongate suitably have a tendency to act like atightly stretched trarnpoline, and thus would lower the shock absorbingeffect of the base layer. It is preferred that the pile fibers beapparently unoriented in the pile fabric, as fibers which are arrangedin a regular or directional pattern tend to give an unwanteddirectionality to the response of the surface to balls, etc., bouncingor rolling thereon. Even distribution of crimped fibers of circularcross section has been found to provide such apparently unorientedpiles.

The base layer should have a thickness of no less than 1A inch, andpreferably `at least 1/2 inch. The quality that appears unique about thebase layers of the present invention is that they are Visco-elastic inthat they provide a retardation to impulse which is not purely elastic(Le. proportional to deformation), but which is also partly viscous(i.e. proportional also to the rate of deformation). Thus the base layerprovides a deceleration rate which is much more nearly uniform than thatprovided by elastic substrates. The base layers of this invention have acoefficient of restitution in the range of 0.05 to 0.3 when using a 1oz. steel weight dropped from a 16-inch drop height onto the surface.The coeflicient of restitution is a measure of the amount of energyreturned to a falling object when it strikes the material. A coeicientof 1.00 would indicate 100% of the energy was returned and 0.00 Wouldindicate no energy was returned. A preferred balance of strength andkinetic properties has been found to occur in materials which have acoefiicient of restitution between 0.1 to 0.2, although the notedbroader range is generally useful. As noted above the room temperatureShore A2 hardness of the base layer resin (without voids or fillers)material should be in the extremely low range of 5 to 40. The optimumhardness range has been found to be about a Shore A2 hardness of to 25.

The polymer used to bond the fabric to the base layer is preferably alsoa two-part polyurethane resin system of the type described above. It maybe preferable to add an organic polyamine such as MOCA to improve thetoughness and cut growth resistance of the polymer. Latex or solventtype adhesive can be substituted for applications where the surfacing isnot anticipated to undergo severe use, but the two part solventfreesystems are greatly preferred for athletic surfacing. The adhesiveshould be applied as a continuous impermeable layer. Because of thesomewhat porous nature of the base layer, the adhesive serves as asealant for the top of the base layer in addition to functioning as anadhesive to secure the pile fabric to the base layer.

While the above described method in which the base layer is poured ontothe substrate and cured in situ is preferred for large athleticsurfaces, for example football fields, it will be understood that inmany applications the surfacing can be prepared by in-plant formation ofa composite base layer to which the pile fabric is adhered as describedabove. Such a lcomposite. can later be applied to the rigid substrate bycasting a relatively thin layer of adhesive, preferably a 100% solidsurethane reaction mixture of the same type from which the base layer isformed. This alternative procedure is particularly advantageous when thesurfacing is applied to relatively small areas, for example golf greensor tee areas, patios, or the like, where it would be impractical toutilize bulky crushing equipment. In -this alternative procedure thecrushing step can be accomplished in the r suppliers plant.

By pile fabric as used herein we mean to include fabrics to whichupstanding fibers are secured by looping, ocking, tufting, etc.

The invention will be further explained with reference to the followingexample in which all parts are given by weight unless otherwiseindicated.

EXAMPLE The following ingredients, designated as Part A were mixed andevacuated separately:

Parts 2000 molecular weight polyoxypropylene glycol 50.33 Litharge 0.20Green chrome oxide-yellow pigment mixture 1.30 Carbon black pigment 0.60Kaolin clay 45.00 Hexogen calcium 0.40

Asbestos fibers, 10 to 35 mesh (Rotap screen analysis) 25,500 cm.2/ gm.surface area by Dyckerhoff system 0.25 Ethylene glycol monoethyleneether (ethyl Cellosolve) 2.10 Phenyl mercurio acetate 0.15

The following ingredients, designated as Part B were mixed separately:

Parts Toluene diisocyanate 86.7

Polyoxypropylene triol 6.0 432 molecular Weight (TP 440) trimethylolpropane 7.3

Approximately eleven parts of B were mixed with one hundred parts of A.Following a thorough mixing of the part A and part B, twenty-seven partsof perlite (average diameter 1A; inch) were blended into the mixture.This mixture was poured over asphalt and screeded to approximately aone-half inch thickness. Following a three hour cure time, the materialwas subjected to a crushing load of approximately 400 p.s.i., repeatedsix times by means of a blunt bladed disc. This provided a soft basewhich exhibited elastico-viscous response to deformation.

A mixture of eleven parts B and one hundred parts A to be used as anadhesive was then spread over the cured, soft base at a rate of gramsper square foot. Immediately the fiber pile top fabric was pressed intoplace so that the curing elastomer mixture wetted the backing fabric andthat portion of the pile fibers in contact with the backing, thusproviding a secure, tenacious bond upon completion of curing. The fiberpile top fabric consisted of a cut crimped nylon pile, 1/2 inch inheight, placed into a knitted polyester backing having a total weight ofapproximately 2.2 pounds per square yard. The individual nylon bers were2 inches long, circular in cross section, heat set crimped with 8 crimpsper inch, so that their length after crimping was about 1 inch, weatherresistant, and approximately 50 denier. The backing is made from 440denier filament polyethylene terephthalate which is circularly knittedon a Wildman Co. knitting machine modified so as to include pile liberin the stitches. The nylon fibers were looped around the backing fiberswith each end forming part of the pile. The pile fabric was lightlycoated. on the back side with an acrylic latex to improve thedimensional stability and handleability of the fabric. The coating waslight enough to just coat the fibers of the backing without closing offthe spaces between the bers.

The physical properties of the construction were tested and found tohave the following values: The base was found to have an elongation atbreak according to ASTM Test D-41261T of 137%, a compression modulusmeasured according to ASTM Test D-575-46 at a strain rate of 20 inchesper minute of 3.17 p.s.i. for 10% compres sion and 40 p.s.i. for 50%compression, a coefficient of restitution as previously described of0.13, and was found not to support the growth of fungi.

The completed surfacing was tested by means of a National Bureau ofStandards machine described in volume 29 of the Journal of Researchwhich was modified to simulate the action of football shoes. One pulleywas used having 50 cleats mounted thereon in three circumferential rows.Each cleat was made of a hard rubber and had a rounded point of 3/16inch radius, which flares out to a radius of 3/8 inch at its base.. Thetopped base distance is three-quarter inch. The surfacing Was subjectedto 30,000 turntable revolutions. Negligible fiber loss was observed. Thefibers were slightly matted in the direction of rotation, but gentlehand brushing restored the pile to substantially its original height. Noloss of adhesion between the base and top was observed, and no damagewas observed in the base layer after 30,000 revolutions.

What is claimed is:

1. An improved synthetic turf comprising a soft elastomeric polyurethanebase layer containing from about 15 to 75% voids by volume and a toplayer of liexible pile fabric, an elastomeric adhesive securing said toplayer and said base layer to one another, said base layer havingVisco-elastic properties, being capable of slow,

gradual and substantially complete recovery from indentation underringer pressure in a period of about 2 to 20 seconds, and having a ShoreA2 scale durometer in the range of 5 to 40 with a coeicient ofrestitution in the range of 0.05 to 0.3 when a l-ounce steel weight isdropped thereon from a 16-inch height.

2. The turf of claim 1 wherein said polyurethane is a cross-linkedpolyalkylene ether based polyurethane.

3. The turf of claim 1 wherein said pile fabric is capable of limitedstretching in any direction.

4. The turf of claim 1 wherein said elastomeric ad hesive ispolyurethane elastomer.

5. The turf of claim 1 wherein said base layer is at least 1A: of aninch thick. f

6. The turf of claim 1 wherein the fibers of said pile fabric arecrimped synthetic bers of generally circular cross section.

7. A method for forming a synthetic turf which comprises (a) forming abase layer of soft Visco-elastic polyurethane elastomer containing fromto 75% by volume of frangible particulate ller, (b) subjecting the baselayer to compressive forces crushing said filler, and

(c) adhering a top layer of eXible pile fabric to said base layer withan elastomeric adhesive.

8. The method of claim 7 wherein said polyurethane elastomer is across-linked polyalkylene ether based polyurethane.

9. An improved synthetic turf comprising a soft elastomeric cross-linkedpolyalkylene ether based polyurethane base layer containing from about15 to 75% voids by volume and a top layer of flexible pile fabriccapable of limited stretching in any direction, an elastomeric adhesivesecuring said top layer and said base layer to one another, said baselayer having Visco-elastic properties, being capable of slow, gradualand substantially complete recovery from indentation under 4fingerpressure in a period of about 2 to 20 seconds, and having a Shore A2scale durometer in the range of 5 to 40 with a coecient of restitutionin the range of 0.05 t0 0.3 when a l-ounce steel weight is droppedthereon from a 16-inch height.

10. An improved synthetic turf comprising a soft elastomericcross-linked polyalkylene ether based polyurethane base layer containingfrom about 15 to 75 voids by volume and a top layer of flexible pilefabric capable of limited stretching in any direction, an elastomericpolyurethane adhesive securing said top layer and said base layer to oneanother, said base layer having Visco-elastic properties, being capableof slow, gradual and substantially complete recovery from indentationunder nger pressure in a period of about 2 to 20 seconds, and having aShore A2 scale durometer in the range of 5 to 40 with a coecient ofrestitution in the range of 0.05 to 0.3 when a l-ounce steel weight isdropped thereon from a l6-inch height.

References Cited UNITED STATES PATENTS 2,515,847 7/1950 Winkler 161-643,325,338 6/1967 Geen 161-89 3,293,723 12/1966 Evans 161-62X 3,312,5834/ 1967 Rochlis 161-62 3,238,156 3/1966 Kohrn 260-25 3,332,828 7/1967Faria et al. 161-21 PHILIP DIER, Primary Examiner U.S. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,597,297 Dated August 3, 1971 Inventods) Theodore Buchnoltz, `Timothy B.Jensen 8c William H.

Penney It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

Column 2, line 39, after "natural" insert soil Column 3, line 55, delete"Cellulose" and insert Cellosolve Signed and sealed this 7th day ofMarch 1972.

(SEAL) Attest:

EDWARD M.FLETQHER,JR. ROBERT GOTTSCHALK Attestlng Offlcer' Commissioner'of Patents ORM DO-1050 (I0-59) uscoMM-Dc eoa7epe9 U,S GOVERNMENTPRINTING OFFICE: 1969 0-366-3S

